Refer to figure.

Draw a diagram:

Draw the circle with 70ºN latitude

Mark the three local meridians

A – 060ºW
B – 060ºE
Greenwich Meridian (000ºE/W) – DATUM meridian

Draw a straight line between A – B, representing the GCT

A and B are of the same latitude => Rhumb line track is 090ºT

The difference between true track at A and B = conversion angle which equals ½ Convergency

Note: on a polar stereographic chart, convergency is always the same to the change in longitude

Convergency = change of longitude
Convergency = 120º
Conversion Angle = ½ x 120º = 60º

At A, GCT < RLT
Therefore, GCT = RLT – conversion angle
GCT = 090ºT – 060º = 030ºT